Diabetes has become a global epidemic. In the United States alone, 26.9% of the population aged 65 years or older suffers from the disease. Foot ulcers are one of the most common complications in diabetics leading to hospitalization. 45-83% of the annual lower extremity amputations in the United States involve diabetics. The direct costs for the treatment of diabetes and its complications in the United States were more than $116 billion in 2007, among which the treatment of foot ulcers accounted for at least 33%.
Foot ulcers are the most common precursor to diabetes-related amputation. Foot ulcer prevention has become the focus of amputation prevention programs. The etiology of ulcerations in people with diabetes is commonly associated with the presence of peripheral neuropathy and unrecognized repetitive trauma.
Foot-care practitioners often use therapeutic shoes and insoles to redistribute the forces on the foot. The standard technique to evaluate their efficacy has been focused on pressure reduction, simply because in-vivo testing of shear in gait lab or clinics is not readily available. Even though peak foot pressures at the site of neuropathic ulceration have been identified as a significant risk factor for foot ulceration, elevated foot pressures are not strongly associated with predicting the development of foot ulcerations in people with diabetes and neuropathy.
The Receiver-Operating Characteristic (ROC) for neuropathic subjects with diabetes indicates that high foot pressures (>87.5 N/cm2) had a sensitivity of 63.5%, a specificity of 46.3%, a positive predictive value of 17.4% and a negative predictive value of 90.4%. This suggests that other pathologic forces on the sole of the foot, such as the shear forces, should be considered in the etiology and prevention strategy for foot ulceration.
Both empirical evidence and basic scientific work support the contribution of shear forces in ulcer development. Unfortunately, attempts to study the effect of shear forces on ulceration is severely handicapped due to the lack of instruments that can measure plantar shear force accurately and conveniently.